Constructed for classroom demonstration, the author's unit was mounted on a mahogany veneer plywood which was sanded and covered with five coats of plastic varnish. Other finishing touches were wood tape veneer around the edges, and nylon casters to make the unit easy to move. The various dimensions of the prototype coil are indicated in the drawing; none is particularly critical. Note that space has been left at each end of the coil, and that stand-off insulators are used to bring out the ends. Nylon screws or glue must be used to fasten top end cover to avoid arcing. After winding coil, cover with many coats of acrylic plastic spray. Spray form first if cardboard is used.